Multiple effect evaporator apparatus

ABSTRACT

A multiple effect evaporator apparatus features a plurality of vertically arranged evaporator chambers, each having a plurality of vertically oriented heat exchange tubes molded at their lower ends to a bottom plate of the chamber and supporting a vessel at their upper ends, said vessel being adapted to receive a solution from an upper chamber, an overflow tube of substantially U-shaped configuration connected at one end to an upper part of the vessel and at the other end being open to the pressure of the next lower chamber, and means for maintaining a pressure difference between the respective chambers.

United States Patent Machida et al.

MULTIPLE EFFECT EVAPORATOR APPARATUS Inventors: Shunichi Machida; Masaharu Tsujita; Shintaro Nakaya; Ryoji Ueno, all of Tokyo, Japan Ebara Manufacturing Co., Ltd., Tokyo, Japan Filed: Apr. 22, 1974 Appl. No.2 462,928

Related US. Application Data Division of Ser. No. 333,035, Feb. 16, 1973, Pat. No,

Assignee:

Foreign Application Priority Data Feb. 16, 1972 Japan 47-16122 US. Cl 159/13 A; 159/18; l59/D1G. 31; 202/174 Int. Cl BOld 1/22; B01d 1/26; BOld 3/02 Field of Search 159/13 A, 18, 13 R; 202/236, 174, DIG. 31

References Cited UNITED STATES PATENTS 2/1900 Harvey 159/18 1,783,464 2/1930 Follair 62/152 2,753,932 7/1956 Eckstrom et 211.... 159/13 A 2,758,061 8/1956 Geller 202/236 X 3,412,778 11/1968 Witt et al 159/13 A 3,481,835 12/1969 Carnavos 159/13 A 3,487,873 l/1970 Bromley et a1. [59/13 A 3,627,646 12/1971 Osdor 159/18 X Primary Examiner-Jack Sofer Attorney, Agent, or Firm-Oblon, Fisher, Spivak, McClelland & Maier [57] ABSTRACT A multiple effect evaporator apparatus features a pinrality of vertically arranged evaporator chambers, each having a plurality of vertically oriented heat exchange tubes molded at their lower ends to a bottom plate of the chamber and supporting a vessel at their upper ends, said vessel being adapted to receive a solution from an upper chamber, an overflow tube of substantially U-shaped configuration connected at one end to an upper part of the vessel and at the other end being open to the pressure of the next lower chamber, and means for maintaining a pressure difference between the respective chambers.

3 Claims, 2 Drawing Figures llIlI lllll/I/I EACAPILLARY TUBE 13 couosusare CONDENSTAE US Patent Sept. 23,1975 Sheet 1 of2 3,907,629

FIG. 1

US Patant Sept. 23,1975 shw 2 of2 3,907,629

VAPOR CAPILLARY TUBE CONDENSATE'.

SOLUTlON CONDENSTAE BACKGROUND OF THEINVENTION 1. Field of the Invention I This invention relates to a multiple effect evaporator apparatus for evaporating and condensing a solution, which is equipped to a chemical or other plant.

2. Description of the Prior Art In conventional multiple effect evaporator apparatus of the type having a plurality of vertically oriented heat exchange tubes disposed in each of two or more evaporator chambers arranged above and below one another with each having a vessel for receiving a solution wherein the upper ends and the lower ends of the heat exchange tubes are each respectively mounted to plates of the adjacent chambers, the difference of pressure levels between the top evaporation chamber and the bottom evaporation chamber provides the force for passing the solution through pressure controlling 'means of each of the chambers.

The pressure reducing function of the different pressure controlling means causes a difference of pressure in each of the chambers, and contributes to attain effective multiple evaporation in normal operation. However, the temperature of the solution is low at the initiation of operation so that the saturated vapor pressure of the solution being supplied is substantially the same as that of the solution at the temperature of the coolant in the bottom chamber, whereby a difference of pressures in the various evaporator chambers is not caused and the pressure reducing function of the different pressure controlling means prevents the flowing of the solution in the heat exchange tubes.

If the heating of the chambersis initiated without a sufficient amount of the solution flowing down through the tubes to wet the inner walls of the heat exchange tubes, the heat exchange tubes will be damaged by heating. Accordingly, the different pressure controlling -means interrupt the operation.

In the conventional multiple effect evaporator apparatus, a required flow of the solution is supplied to the 'heat exchange tubes by the liquid pressure achieved by increasing the depth of the solution in the evaporator. However, it has been found that more than 3 meters of depth of the solution in the evaporator is required in the case where the maximum temperature of the solution is about 120C and the effective steps are about in number. However, the length of the heat exchange tubes is usually about 3m. Accordingly, the depth of ;the vessel is substantially the same as the length of the heat exchange tube, so as to occupy similar space, 'which is quite uneconomical, whereby remarkably expensive construction cost of the apparatus is required.

Moreover, it is difficult to control the evaporation caipacities of the chambers, so that the solution overflows into the condensed water because of flow rate control difficulty and a safe operation cannot readily be expected.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention .to provide an improved multiple effect evaporator apparatus which can be safely operated withoutany trouble at the initiation of operation and can keep a suitable differential pressure so as to improve the coefficient of evaporation.

It is another object of this invention to provide an economical and compact multiple effect evaporator apparatus wherein evaporation effects of the chambers can be easily controlled so as to increase the range of control of amounts of evaporation and to decrease the depth of the vessel.

'vertically oriented heat exchange tubes being mounted to an upper plate at their top ends and to a bottom plate at their lower ends for increasing the evaporation coefficient in each of the evaporator chambers, a vessel for receiving a solution disposed above each of the upper plates with each of the upper plates comprising the respective vessel bottom, a siphon overflow tube in each chamber having one end thereof connected to an overflow outlet of the vessel, thus controlling the depth of solution therein and thus open to its chamber so as to be subject to its chamber pressure and the other end being connected to the lower plate as an outlet of the solution from the overflow tube and thereby being open to the pressure of the next lower chamber, whereby an undesired flow over the brim of each vessel to its respective bottom plate is prevented so as to prevent a contamination of the resulting condensate with the undesired brim overflow solution, with the siphon overflow tubes receiving the solution under differential heads so as to overflow the solution regardless of the pressure difference between successive chambers.

In accordance with the multiple effect evaporator apparatus of the present invention, an excess of the solution flows down to the next lower chamber through the siphonic overflow tube so as to prevent overflow of the solution over the brim of the vessel to the bottom of the condenser chamber and so as to maintain the pressure difference between the upper chamber and the lower chamber by forming siphonic solution column. The term of siphon tube in the context of this disclosure means any form of tube acting as a siphonic liquid column which maintains different pressures between one end and the other end of the tube. Accordingly, the tube can be of such shapes as shown below:

OJIO (0" BRIEF DESCRIPTION OF THE DRAWINGS Various other objects, features and attendant advantages of this invention will be more readily appreciated as the same becomes better understood from the fol lowing detailed description, when considered in connection with the-accompanying drawings, wherein:

FIG. 1 is a sectional elevational view of one embodiment of a multiple effect evaporator apparatus according to this invention; and

FIG. 2 isa sectional elevational view of another embodiment of the apparatus according to this invention.

- DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, wherein like reference numerals designate like or corresponding parts throughout the several views, and more particularly to FIG. 1, a plurality of evaporator chambers 4 disposed one above the other are separately formed by dividing a casing 11 with horizontal plates 10 so as to form the multiple effect evaporator apparatus. 1

A plurality of heat exchange tubes 3 are vertically arranged in each of the chambers 4 being open at the lower ends thereof through the respective plates. 10. Above the heat exchange tubes 3, a vessel 1 for receiving 'a solution is mounted thereto through a plate 10, being equipped with a pressure difference maintaining means in the form of a dividing wall 8 having a resistant orifice 18 therein and a solution distributing means in the form of an apertured wall 9 arranged beneath the wall 8 and above the plate 10', through which the upper ends of the heat exchange tubes 3 open.

An overflow outlet 5 in FIG. 1 is formed in the vessel l at a place controlling the depth of the solution therein. An overflow tube 2 connected at one end to the overflow outlet 5 has a substantially U-shaped configuration so as to maintain the solution as a U-shaped liquid column 7, and an outlet 6 at the other end of the overflow tube 2 is connected to the vessel 1 through the apertured wall 9, so as to be open therethrough via the vertical heat exchange tubes 3 to the next lower chamber 4, so as to have the lower chamber pressure.

A part of the solution Q received in the vessels flows down through the resistant orifice 18 to the next lower chamber, and is reduced in pressure when it passes through the resistant orifice, to provide the difference of pressure. All of the remainder of the solution Q received in the vessel 1 above the wall 8 flows through the overflow tube 2 to the lower part of the vessel 1 between the wall 8 and the wall 9, and the U-shaped liquid column 7 is thus formed therebetween.

In FIG. 2, where another embodiment of the multiple effect evaporator apparatus is shown, a pressure difference maintaining means is connected to a solution distributing means as an integral body, so that the pressure reducing and solution distributing means 9 is formed at the inlets of the heat exchange tubes 3. The outlet 6 of the overflow tube 2 in this case is placed above the vessel 1 of the next lower evaporation chamber 4.

In accordance with this embodiment, most of the so-? lution Q is supplied by passing through the pressure reducing and solution distributing means 9 to the heat exchange tubes 3 in a normal operation. Only an amount of the solution necessary for keeping the solution in the U-shaped tube 7 is supplied through a capillary tube 12 for supplying a pressure sealing solution. Thus, the overflow tube 2 is operated as a safety device when the height of the solution rises because of trouble in controlling the flow rate of solution Q at the initiation of operation. Accordingly, it is a quite effective system for increasing safety compared with the conventional vertical type evaporator apparatus.

Also, in FIG. 2, the reference numeral 13 designates an outlet of condensed water; Q designates. an original solution; S designates a vapor; P and P designate pressure in each of the vapor chambers; and h and h designate the differences of head in the U-shaped tubes 2 of an upper and lower chamber 4 for maintaining different pressures therein.

In order to control the vapor pressures in each of the evaporator chambers of the preferred embodiments of the invention and to increase the heat exchange coefficient of the heat exchange tubes, it is possible to form a noncondensed gas passage from the upper evaporation chamber to the lower evaporation chamber. This noncondensed gas passage. can beat verticle tubular member 25 arranged between plates and the' lower plates of the vessels 1 hermetically sealed at its upper end and having a plurality of fine holes 26 therein and a bottom opening 27 and ispreferably placed at the tion chamber.

In accordance with the vertical multiple effect evaporator apparatus shown inFlG. l, the vapor S evaporated in an upper evaporator chamber is supplied to the evaporator chamber 4 around the heat exchange tubes 3 and is used as a heat source for the next lower evaporator chamber and the unevaporated solution Q is supplied to the vessel 1 in the lower evaporator chamber flowing down through the heat exchange tubes 3 through the pressure difference maintaining means 8 and the solution distributing means 9. When the solution Q is passed through the pressure difference maintaining means 8, the pressure is reduced so that the solution in the lower evaporator chamber is evaporated and condensed at a lower temperature than the solution in the upper evaporator chamber. In normal operation, the solution Q heated at the top evaporator chamber is evaporated until reaching saturated vapor pressure at the corresponding temperature so that the pressure is maintained.

On the other hand, the vapor in the bottom evaporator chamber is condensed by cooling with a coolant water so that the vapor pressure corresponds to the cooling effect of the coolant water.

The pressure difference resulting from the difference of saturated pressures in the top chamber and the bottom chamber provides the power source and a predetermined rate of solution passes through each pressure difference maintaining means 8 in each chamber, so

that the pressure differences in the chambers are caused by the pressure reducing function. The temperature of the solution is decreased by evaporation so that the saturated vapor pressure is changed in each chamber and is balanced by the pressure reducing function, thereby holdingthe normal operation.

A part of the solution Q received on the pressure difference maintaining walls 8 is passed through the resistance orifices 18 and the remainder of the solution Q is supplied through the overflow outlet 5, to the overflow tube 2 to form the U-shap'ed solution column 7 therein.

The difference of heads 11 of the U-shaped solution column is changed so as to compensate for the pressure difference between the upper part and the lower part of the pressure difference maintaining means 8. The following equation is given:

wherein P designates the pressure of the upper cham-* ber, P designates the pressure of alower chamber and y designates specific gravity of the solution, RP and 11 being in meters.

When the solution is supplied to the right end of the U-shaped solution column, the right end tends to rise so as to decrease h, but the solution flows down from the left end to the lower part of the vessel below the pressure difference maintaining means 8 corresponding to the amount of solution supplied, whereby the difference of head 11 is maintained and the pressure difference (P-Po) is not affected, Po being an original pressure.

The solution 0 flows down through the overflow tube 2 and is added to the solution passing through the resistance orifices 18 of the pressure difference maintaining means 8 and uniformly flows down through the distribution means 9 into the heat exchange tubes 3. The amount of solution passing through resistance orifices 18 is dependent upon the pressure difference (P-Po) and the depth of the solution in vessel 1. The 'depth of the solution is constant and is not affected by a change of the feed rate of the solution Q, because of the overflow tube 2.

Accordingly, the amount of solution passed through the resistance orifices of the pressure difference maintaining means 8 is dependent upon only the pressure difference PP0, and thus is decided by the saturated vapor pressures at the temperatures of the solutions in the top chamber and in the bottom chamber. The pressure difference in the multiple effect evaporator apparatus system is distributed to be proportional to each pass resistance of the pressure difference maintaining means 8 in each chamber. The pressure difference P-P between adjacent chambers has close connection to the evaporation coefficient of each chamber.

Further, in accordance with the multiple effect evaporator apparatus of this invention, the pressure differences P--P between adjacent chambers and the evaporation coefficient of each chamber can be controlled by selecting the temperature of the solution in the top chamber, so that the control system is quite simple.

Also, any excess of solution flows down through the overflow tube, so that the overflow of the solution from the vessel to the bottom of the evaporator chamber is prevented, and the rate of solution flow can be changed in a wide range without affecting the depth of the solution in the vessel and the pass resistance of the pressure difference maintaining means by forming Ushaped solution column in the overflow tube so as to maintain the pressure difference.

Furthermore, the evaporation coefficient of each chamber can be easily controlled so as to increase the range of control of the rate of evaporation, and the depth of solution in the vessel can be remarkably decreased so that the construction cost of the apparatus can be decreased. It is also possible to prevent excess rise of the surface of the solution in the vessel placed .above the heat exchange tubes caused by a change of the rate of flow of solution and the pressure difference, whereby the contamination of the condensed water with the solution overflowing from the vessel by the excess rise, can be prevented, and a safe operation is kept even though flow rate difficulty occurs. The evaporation coefficient is improved without any deterioration of the function of evaporation and the control of each of the evaporator chambers is remarkably simplified and the maintenance of the apparatus is simple.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claim, the invention may be practiced otherwise than as specifically described herein.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A multiple effect evaporator apparatus which comprises:

a plurality of evaporator chambers disposed in vertical alignment;

a plurality of thin falling internal film type vertically oriented heat exchange tube bundles for increasing evaporation coefficient in each of said evaporator chambers;

said heat exchange tubes being molded to an upper plate at the top ends and to a bottom plate at the lower ends thereof;

a vessel for receiving solution placed above said upper plate in each of said chambers;

pressure difference maintaining means for maintaining difference of pressure between said evaporator chambers in the solution flow path;

a siphon overflow tube having one end thereof connected to an overflow outlet of said vessel above said pressure difference maintaining means at a place controlling the depth of said solution in said vessel and being open to the chamber containing said vessel, and the other end of said tube being connected to the bottom plate above the vessel in the next lower evaporator chamber as an outlet of said solution from said overflow tube to said lower vessel so as to maintain the pressure difference between the upper and lower chambers, whereby an overflow from said vessel over its brim to said bottom plate of its condensing chamber is prevented so as to prevent contamination of the resulting condensate with said solution; and

said overflow tube receiving said solution under a differential head so as to overflow said solution, regardless of the pressure difference in each chamher.

2. The multiple effect evaporator apparatus according to claim 1, further comprising a non-condensible gas passage from the upper evaporation chamber to the next lower evaporation chamber, including a tube in said bundle sealed from the vessel and containing perforations above the condensate level, whereby a portion of the vapor contacting said heat exchange tubes is passed to the next lower evaporation chamber along with the non-condensible gases.

3. The multiple effect evaporator apparatus according to claim 1 wherein a capillary tube for supplying a pressure sealing solution in the siphon overflow tube connects the vessel between the bottom thereof and the overflow outlet to the siphon overflow tube at its upper 

1. A MULTIPLE EFFECT EVAPORATOR APPARATUS WHICH COMPRISES: A PLURALITY OF EVAPORATOR CHAMBERS DISPOSED IN VERTICAL ALINGMENT, A PLURALITY OF TIN FALLING INTERNAL FILM TYPE VERTICALLY ORIENTTED HEAT EXCHANGE TUBE BUNDLES FOR INCREASING EVAPORATION COEFFICIENT IN EACH OF SAID EVAPORATOR CHAMBERS, SAID HEAT EXCHANGE TUBES BEING MOLDED TO AN UPPER PLATE AT THE TOP ENDS AND TO A BOTTOM PLATE AT THE LOWER ENDS THEREOF, A VESSEL FOR RECEIVING SOLUTION PLACED ABOVE SAID UPPER PLATE IN EACH OF SAID CHAMBER, PRESSURE DIFFERENCE MAINTAINING MEANS FOR MAINTAINING DIFFERENCE OF PRESSURE BETWEEN SAID EVAPORATOR CHAMBERS IN THE SOLUTION FLOW PATH, A SIPHON OVERFLOW TUBE HAVING ONE END THEREOF CONNECTED TO AN OVERFLOW OUTLET OF SAID VESSEL ABOVE SAID PRESSURE DIFFERENCE MAINTAINING MEANS AT A PLACE CONTROLLING THE DEPTH OF SAID SOLUTION IN SAID VESSEL AND BEING OPEN TO THE CHAMBER CONTAINING SAID VESSEL, AND THE OTHER END OF SAID TUBE BEING CONNECTED TO THE BOTTOM PLATE ABOVE THE VESSEL IN THE NEXT LOWER EVAPORATOR CHAMBER AS AN OUTLET OF SAID SOLUTION FROM SAID OVERFLOW TUBE TO SAID LOWER VESSEL SO AS TO MAINTAIN THE PRESSURE DIFFERENCE BETWEEN THE UPPER AND LOWER CHAMBERS, WHEREBY AN OVERFLOW FROM SAID VESSEL OVER ITS BRIM TO SAID BOTTOM PLATE OF ITS CONDENSING CHAMBER IS PREVENTED SO AS TO PREVENT CONTAMINATION OF THE RESULTING CONDENSATE WITH SAID SOLUTION, AND SAID OVERFLOW TUBE RECEIVING SAID SOLUTION UNDER A DIFFERENTIAL HEAD SO AS TO OVERFLOW SAID SOLUTION, REGARDLESS OF THE PRESSURE DIFFERENCE IN EACH CHAMBER.
 2. The multiple effect evaporator apparatus according to claim 1, further comprising a non-condensible gas passage from the upper evaporation chamber to the next lower evaporation chamber, including a tube in said bundle sealed from the vessel and containing perforations above the condensate level, whereby a portion of the vapor contacting said heat exchange tubes is passed to the next lower evaporation chamber along with the non-condensible gases.
 3. The multiple effect evaporator apparatus according to claim 1 wherein a capillary tube for supplying a pressure sealing solution in the siphon overflow tube connects the vessel between the bottom thereof and the overflow outlet to the siphon overflow tube at its upper end. 